Macromolecular structure determination using electron microscopy has become a useful research tool aimed at understanding biological processes, identifying conformational changes, and characterizing components in cellular pathways. Our long-term goal is to broaden the group of people able to determine macromolecular structures by providing integrated, easy to use, and efficient software for routine determination of three-dimensional macromolecular structures using electron microscopy. Novel aspects of this software include an expert system to guide users through the reconstruction process, multiple efficiently coded algorithms, and integrated data analysis and visualization tools. In addition, by incorporating this software into Tumbleweed, our software site for electron microscopy data processing, we will provide a consistent, easy to use graphical user interface; data analysis, data management, and data logging tools; and the availability of additional structure determination methods provided by Tumbleweed. The result of this Phase I SBIR will be a design specification for this integrated software package allowing easy, efficient, and routine determination of macromolecular structures by biomedical research scientists and structural biologists. Furthermore, one aspect of the reconstruction procedure will be targeted for development as a prototype to demonstrate project feasibility. The complete suite will be implemented and tested in a Phase II SBIR. PROPOSED COMMERCIAL APPLICATION: Single Particle umbleweed targets users with varied knowledge, experience, and research goals. Biochemists and cell and molecular biologists will be attracted to the user guidance and ease of use that will allow them to perform their own structural studies. Structural biologists will be attracted to a complete integrated software package that allows all aspects of single particle reconstruction and analysis to be performed in a single extendible package. Combined these groups will provide a large user-base allowing OED Labs to sucessfully commercialize Single Particle Tumbleweed